Hi there,
Sorry to hear about this. Would you mind sharing the version of the Illustrator?
In addition to suggestions given earlier, please try troubleshooting suggested on this help article(https://helpx.adobe.com/no/fonts/kb/troubleshoot-font-activation.ug.html) to resolve font issues.
If it doesn't help, you may follow suggestions given on this community post(https://community.adobe.com/t5/illustrator/resolve-slow-performance-and-unexpected-behaviors-in-illustrator/td-p/11561981).
Hope it helps.
Regards,
Ashutosh
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